Method for forming heat-resistant containers

ABSTRACT

A heat-resistant container forming method includes a step of thermally shrinking a primary blow molded article in a heating furnace before secondary blow molding the primary blow molded article into a final product or container. Into the furnace, hot air which flows along the longitudinal direction of the first blow molded article and whose temperature enough to facilitate crystallization of the primary blow molded article. The primary blow molded article is thermally shrunk by exposing the entire circumferential surface of a barrel of the primary blow article to the hot air and by blowing the hot air longitudinally along the primary blow molded article to heat the barrel circumferentially uniformly. Since hot air touches the barrel as flowing longitudinally thereof, it is possible to increase the heat conductivity of boundary film of the primary blow molded article, without increasing the hot air temperature too high, so that temperature rise of the primary blow molded article is facilitated.

This is a division of application Ser. No. 08/134,799 filed Oct. 12,1993 now U.S. Pat. No. 5,445,415.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for forming aheat-resistant synthetic resin container, and more particularly to sucha method and apparatus in which a barrel and shoulder portions of aprimary blow molded article is heated uniformly in a short time beforesecondary blow molding.

2. Description of the Related Art

Generally, a thin synthetic resin packing container called "a biaxiallyoriented blow container" is formed by placing in the mold an injectionor extrusion molded preform of a suitable temperature for stretching andthen by stretching the preform vertically or longitudinally whileexpanding the preform transversely with the pressure of gas blown intothe preform.

However, the above-mentioned conventional container has a problem thatthe barrel portion of the container made of certain kinds of materialwould be deformed on filling up with the contents of high temperature.

Consequently a so-called oven blow molding method is proposed. In thisconventional molding method, the blow molding step to be carried outafter temperature control of the preform is divided into primary andsecondary subdivided steps. In the primary blow molding, the article isformed so as to be longer than the final product to be obtained in thesecondary blow molding. This primary blow molded article is thenthermally shrunk by heat treatment, whereupon this article is secondaryblow molded to form a final product. According to this conventionalmethod, it is possible to obtain a heat-resistant container whose heatresistance is improved by heat treatment before the secondary blowmolding.

FIG. 16 shows an article obtained by the oven blow molding. This ovenblow molding method, as described in detail in, for example, JapanesePatent Laid-Open Publications Nos. HEI 3-205124 and HEI 3-234520, whichare applicant's prior applications, comprises the step of obtaining aprimary blow molded article 70 after temperature control of an injectionor extrusion molded preform 60 having a suitable temperature forstretching, the step of obtaining a thermally shrunk article 80, and thestep of obtaining a secondary blow molded product 90, the material ofthe preform 60 being polyethylene terephthalate (hereinafter abbreviatedas PET), for example.

Specifically, the primary blow molded article 70 is obtained bystretching the preform 60 longitudinally with centering-guiding by astretch rod (not shown) inserted into the preform 60 from its neckportion and, at the same time by expanding the longitudinally stretchedpreform 60 transversely by injecting pressurized fluid such as air intothe preform 60.

The thermally shrunk article 80 is obtained by thermally shrinking theprimary blow molded article 70 longitudinally and transversely byheating the article 70 in the atmosphere of 180° C. to 280° C. Thethermally shrunk article 80 has a height substantially equal to orslightly longer than that of the final product, and a transverse sizesmaller than that of the final product.

The secondary blow molded product 90 is obtained by placing thethermally shrunk article 80 in the cavity of a secondary blow mold formolding the final product and then by introducing air into the thermallyshrunk article 80 to be stretched transversely.

According to the oven blow molding method, during the heat treatmentstep to be carried out before the secondary blow molding, distortioncreated in the primary blow molding step is eliminated to increase thedegree of crystallization so that the article will be resistant tosevere temperature condition in the second blow molding step.

In order to obtain such a heat-resistant container, it is necessary toraise the temperature of the molded article to such an extent that thedegree of crystallization can be improved.

However, in the conventional heating furnace, conventional heat transferalone to the molded article in the atmosphere is insufficient for smoothraise of the temperature.

Since it would take a long time to get the temperature to a sufficientlylevel to obtain a certain degree of crystallization for adequate heatresistance of the article, it is required to lengthen the travellingpath of the heated article or to protract the heating time, so that themolding apparatus including the travelling path for heating would belarger in size or the molding cycle would be longer.

In such heat treatment, it is also required to shrink the entire primaryblow molded article uniformly to reduce the molding time during thesecondary blow molding and to cause uniform heat resistance.

Practically on some occasions, however, the preform after temperaturecontrol would not retain a uniform circumferential temperaturedistribution. When the preform without a uniform circumferentialtemperature distribution undergoes the primary blow molding, the extentof circumferential stretch would vary locally to cause irregular wallthickness. Therefore, as the primary blow molded article having suchnon-uniform thickness is thermally treated, uniform thermal shrinking inthe circumferential direction cannot be achieved. On some occasions, thecircumferential shrinking would be irregular depending on the directionof hot air blow in the oven, and/or the coefficient of contraction wouldvary due to the difference in axial stretching magnification and wallthickness. When the thermally shrunk article is placed in the cavity andthe mold is clamped for the second blow molding, the less shrunk portionwould be sandwiched between the parting surfaces of the secondary blowmold and would be partly left as fins. Because of fins, the secondaryblow molded article as the final product are used to be disposed of as afault so that the yield of the heat-resistant container might beimpaired.

SUMMARY OF THE INVENTION

With the conventional problems in view, it is an object of thisinvention to provide a heat-resistant container forming method which canreduce a time necessary to increase the temperature of a primary blowmolded article so that a molding apparatus having a travelling path tobe heated can be prevented from being large-sized.

Another object of the invention is to provide a heat-resistant containerforming apparatus which can prevent part of a primary blow moldedarticle from being sandwiched between the parting surfaces of asecondary blow mold to form fins when the thermally treated primary blowmolded article is placed in the cavity of the mold, thus improving theyield of the container as a final product.

According to a first aspect of the invention, there is provided a methodof forming a heat-resistant container, comprising the steps of:introducing a primary blow molded article into a heating furnace;thermally shrinking the primary blow molded article by exposing theentire circumferential surface of a barrel portion of the primary blowarticle to hot air having a temperature high enough to facilitatecrystallization of the primary blow molded article by blowing the hotair longitudinally along the primary blow molded article; and secondaryblow molding the thermally molded primary blow molded article in acavity of a secondary blow mold composed of a pair of mold halves,thereby shaping the primary blow molded article into the heat-resistantcontainer.

According to a second aspect of the invention, there is provided anapparatus for forming a heat-resistant container by thermally shrinkinga primary blow molded article in a heating furnace and then secondaryblow molding,

wherein the heating furnace includes a hot air blow generator forblowing hot air at a given wind speed, whose temperature is such as tofacilitate crystallization of the primary blow molded article, a firstair blow guide member situated around a barrel portion of the primaryblow molded article and extending longitudinally of the primary blowmolded article, and an air supply port for supplying the hot air fromthe hot air blow generator inwardly of the first air blow guide memberfrom the side of one end thereof, whereby the primary blow moldedarticle is thermally shrunk by being blown by the hot air at a givenwind speed longitudinally along the primary blow molded article whileexposing the entire circumferential surface of a barrel portion of theprimary blow article to the hot air and then guiding the hot air throughthe first air blow guide member.

With the method and apparatus of this invention, when thermallyshrinking the primary blow molded article, the boundary film heatconductivity of the primary blow molded article is increased by movingthe ejected hot air longitudinally along primary blow molded article, sothat the amount of heat for the primary blow molded article receives isincreased. Namely, a heating time can be reduced, which is necessary tosecure an adequate degree of crystallization for obtaining a heatresistance for the final product. In addition, since hot air flowslongitudinally along the primary blow molded article, the barrel can beheated circumferentially uniformly so that any irregular thickness canbe prevented by thermal shrinking. The temperature to facilitatecrystallization of the primary blow molded article is in a range ofabout 120° to 240° C., and the temperature of hot air is about 180° to280° C. so as to increase the temperature of the primary blow moldedarticle to the range.

Preferably, the first air blow guide members are situated on oppositesides of the travelling path of the primary blow molded article in theheating furnace, the hot air from the hot air blow generator is blownlongitudinally along the primary blow molded article from one end towardthe other inside the first air blow guide member. Further, the hot airafter touching the barrel of the primary blow molded article may becollected in the hot air blow generator. In this case, the first airblow guide members serve as a guide for guiding hot air blowlongitudinally along the primary blow molded article, and also as apartition dividing the air blow passageway into two: a first subdividedpassageway for supplying hot air from the hot air blow generator and asecond subdivided passageway for collecting hot air in the hot air blowgenerator.

A second air blow guide member may be situated opposite to the bottom ofthe primary blow molded article in the heating furnace for masking thebottom when the hot air from the hot air generator is blown upwardlyfrom the bottom side of the primary blow molded article. With the secondair blow guide member, it is possible to guide the hot air to the barrelwhile preventing the hot air from directly touching the bottom. It isthereby possible to prevent the bottom from being white-crystallized asexcessively heated, so that the barrel can be heated efficiently.

A third air blow guide member may be situated around the shoulder of theprimary blow molded article, sloping in conformity to the slope of theshoulder, so that the hot air can pass along the shoulder. It is therebypossible to increase the degree of crystallization of the shoulderhaving a low stretchability, and hence to improve the heat resistance.

Hot air may be blown over the primary blow molded article from theshoulder toward the barrel. In this case, hot air can be blown along theshoulder, without using the second and third air blow guide members, sothat the hot air is prevented from directly touching the bottom.

By varying the wind speed and/or temperature of hot air, it is possibleto control the heating time in such a manner that the density of thebarrel necessary to secure heat resistance is at least 1.373 g/cm³. Inorder to improve the heating efficiency by the change of boundary filmheat conductivity and not to excessively increase the temperature of hotair, it is preferable that the wind speed of hot air is at least 0.6m/sec. According to experiments, when the temperature and wind speed ofhot air were set respectively to 230° to 260° C. and 0.6 to 4.0 m/sec,it was possible to reduce the heating time to at most one minute for thebarrel to have a density of at least 1.373 g/cm³.

In the thermally shrinking step immediately before the primary blowmolding step, the confronting sidewalls of the primary blow moldedarticle may be pressed inwardly to reform the outer diameter of theprimary blow molded article in the direction parallel to the partingsurfaces of the second blow mold so as to be smaller than the horizontalwidth of the mold cavity. Even if there is a difference in outerdiameter of the primary blow molded article circumferentially due to thedifference in extent of shrinking in the heat treatment, any part of thethermally shrunk article can be protected from being sandwiched betweenthe mold halves when the mold is closed.

In this reforming step, when the increased inner pressure as theconfronting sidewalls of the primary blow molded article are pressed isreleased, the size is corrected smoothly. The reforming step shouldpreferably be performed under temperature control; it can thereforeprevent the part of the primary blow molded article in contact with thereforming means from being excessively cooled or heated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing an entire oven blow stage in an oven blowmolding apparatus for carrying out a container forming method of thisinvention;

FIG. 2 is a fragmentary cross-sectional view showing the structure of aheating furnace mounted in the oven blow stage of FIG. 1;

FIG. 3 is a characteristic diagram showing a relationship between thehot air generating conditions in the heating furnace of FIG. 2 and thedegree of crystallization of a container under such conditions;

FIG. 4 is a fragmentary diagram showing a modified heating furnace;

FIG. 5 is a fragmentary diagram showing another modified heatingfurnace;

FIG. 6 is a diagram showing the heating furnace and a container widthreforming means in the oven blow stage of FIG. 1;

FIG. 7 is a fragmentary plan view of the container width reforming meansof FIG. 6;

FIG. 8 is a perspective view showing reforming guides to be used in thecontainer width reforming unit of FIG. 6;

FIG. 9 is a fragmentary perspective view showing a blow mold clampingmeans to be used in the oven blow stage of FIG. 1;

FIG. 10 is a diagram showing one form of the blow mold clamping means ofFIG. 9;

FIG. 11 is a diagram showing a conventional mold clamping means to beused in the oven blow stage of FIG. 1;

FIG. 12 is a schematic view showing a conventional secondary blow moldclamping means;

FIG. 13A is a plan view showing one example of conventional secondaryblow mold lock members;

FIG. 13B is a plan view showing the operation of the conventionalsecondary blow mold lock members of FIG. 13A;

FIG. 14 is a diagram showing a discharge station and a discharge meansin the oven blow stage of FIG. 1;

FIG. 15 is a schematic view showing a sorting structure for sortingqualified articles and fault articles from one another in the dischargestation of FIG. 14; and

FIG. 16 is a schematic view showing a preform, articles and a finalproduct according to the oven blow molding apparatus.

DETAILED DESCRIPTION

Details of this invention will now be described with reference to theaccompanying drawings. Reference numerals designated to the articles areused the ones which are shown in FIG. 16.

This invention is characterized by facilitating temperature rise of thebarrel of a primary blow molded article by accelerating heat conductionof air using hot air blow.

Specifically, the amount of heat to be received in the barrel isobtained by the following equation:

    Q=A·U·Δt

where Q is the amount of heat, A is the surface area, U is the generalheat conductivity to be obtained from the boundary film heatconductivity, and Δt is the temperature difference.

Therefore, by increasing the general heat conductivity, it is possibleto increase the amount of heat to be received by the barrel. In thisinvention, aiming at the fact that the boundary film heat conductivityinfluence on the general heat conductivity varies according to the windspeed of hot air, the amount of heat is increased by increasing theboundary film heat conductivity by accelerating the wind speed of hotair somehow.

In this invention, reduction of the time necessary to increase thedegree of crystallization in the barrel of a primary blow molded articleis facilitated by accelerating the temperature rise in the barrelaccording to the above-mentioned heat quantity increasing system.

An embodiment of a heat-resistant container forming apparatus using theabove-mentioned principles will now be described with reference to thedrawings.

FIG. 1 is a plan view showing an oven blow stage 20 of an oven blowmolding apparatus 10 embodying this invention. In the oven blow stage20, a rotary disc 22 is mounted on a frame of the oven blow moldingapparatus 10.

The rotary disc 22 is intermittently rotatable in the direction of anarrow. On the rotating path of the rotary disc 22, there is situated aconveying station 12 having a travelling path for primary blow moldedarticles 70, and a discharge station 14 having a discharge path forsecondary blow molded articles 90. Between these two stations, there arelocated first to fifth heating stations 24A to 24E and a secondary blowmolding station 30. In the secondary blow molding station 30, a moldclamping means 32 having a secondary blow mold composed of mold halvesis situated.

The rotary disc 22 has a structure for holding the neck of each articlewhile a number of articles are moved to the individual station. Thisholding structure is exemplified by a cap member described in JapanesePatent Laid-Open Publication No. HEI 3-234520. Though it will bedescribed later, in this embodiment, the cap member is in the form of ablock for holding a set of four articles arranged along the periphery ofthe rotary disc 22. The rotary disc 22 is intermittently driven forrotation upon every termination of the second blow molding. Therefore,each set of four articles will be conveyed at once by one step.

In the conveying station 12 and the discharge station 14, there aresituated respectively a supply means 16 and a discharge means 18 whichare reciprocatingly movable toward and away from the rotary disc 22.

On the other hand, a heating furnace 240 to be used in the first tofifth heating stations 24A to 24E, as shown in FIG. 2, is opening at itsupper portion and has a partition (first air blow guide member) 240Adividing the interior into an inner space 240B and an outer space 240C.The partition 240A is located on each side of the travelling path ofarticles at each station 24A to 24E.

Each space is connected at its lower portion to a hot air blow generator240F via air pipes 240D, 240E. The spaces communicate with each othervia the open upper portion of the partition 240A. The hot air blowgenerator 240F is attached to the side portion of the molding apparatus10; the hot air from the hot air blow generator 240F passes the air pipe240D connected with the inner space 240B, is ejected from the lowerportion of the inner space 240B, and is then returned to the hot airblow generator 240F en route the outer space 240C and the air pipe 240Evia the open upper portion of the partition 240A.

Situated under the inner space 240B and the bottom 74 of the primaryblow molded article 70 hanging in the space is a second air blow guidemember 240G having a tray-shape cross section and has such a shape as toguide the hot air blow toward the barrel 72 of the primary blow moldedarticle 70. The second air blow guide member 240G prevents the hot air,which is ejected from the hot air blow generator 240F, from being blownagainst the bottom 74 of the primary blow molded article 70. In eachstation 24A to 24E, the second air blow guide member 240G is situated ina lower position confronting the article stopped after movingintermittently. Alternatively, the second air blow guide member 240G maybe in the form of guide blades to facilitate blowing the hot air in thecircumferential direction.

At the partition 240A facing the shoulder 76 of the primary blow moldedarticle 70, there is situated a third air blow guide member 240Hextending into the inner space at an angle corresponding to the angle ofinclination of the shoulder 76 so that the hot air flowing from thelower portion of the inner space 240B will be guided along the shoulder76 of the primary blow molded article 70.

In this embodiment, the wind speed and temperature of the hot airejected from the hot air blow generator 240F are set as follows:

It is a common knowledge that the density of material for a finalproduct 90 to be obtained by the second blow molding should be at least1.373 g/cm³ in order to maintain the heat resistance of a thin containeras the final product. In this embodiment, the wind speed and temperatureof hot air are set to values to satisfy this condition.

FIG. 3 shows two kinds of wind speed/temperature conditions for securingadequate density. FIG. 3 is a table showing the degrees ofcrystallization at various portions of the barrel of the primary blowmolded article 70 obtained for the heating time that was obtained fromthe wind speed and temperature of hot air ejected from the hot air blowgenerator 240F.

As is apparent from FIG. 3, when the wind speed of hot air wasrelatively low or 0.6 m/sec and the heating temperature was necessarilyhigh or 260° C., the degree of crystallization at each portion of thebarrel 72 was obtained, in a relatively short time of one minute, insuch a value as to satisfy the adequate density.

On the other hand, when the wind speed of hot air was increased to 4m/sec, the substantially same degree of crystallization at variousportions of the barrel 72 as that of the case of high temperatureheating was obtained in a reduced heating time of 30 sec even at a lowheating temperature of 230° C.

The degree of crystallization of the barrel 72 was obtained by heatingthe primary blow molded article up to 180° to 220° C. As is apparentfrom experimental data of FIG. 3, the slower the wind speed, a higherthe hot air temperature is required. Partly since the apparatus would besubject to trouble when the temperature of hot air is too high, andpartly since the increase of amount of heat due to the change of theboundary film conductivity when the wind speed of hot air is too small,it is preferable that the wind speed of hot air should be at least 0.6m/sec.

The heating time for the primary blow molded article 70, as is apparentfrom the experimental data of FIG. 3, may be controlled by varying thewind speed and/or temperature of hot air.

The heating time is made shorter than conventional by adjusting the twoparameters of hot air, and as a result, it is possible to make the totallength of the heating furnaces 24A to 24E, where the primary blow moldedarticles 70 is heated, shorter than conventional. Even though thesecondary blow molding cycle varies resulting from different shapes,etc. of articles, it is possible to cope with it easily by changing theheating time by adjusting the two parameters of hot air, withoutchanging the total length of the heating furnaces 24A to 24E, thusimproving the versatility.

With this arrangement, the hot air supplied from the hot air blowgenerator 240F is ejected from the lower portion of the inner space 240Bin the heating furnace 240 at the wind speed of at least 0.6 m/sec. Theejected hot air flows around toward the barrel 72 of the primary blowmolded article 70, touching the second air blow guide member 240G toavoid direct touch with the bottom 74. Then the hot air flows near theshoulder 76 along the primary blow molded article 70 as guided by thepartition or first air blow guide member 240A. The hot air reached nearthe shoulder 76 flows along the shoulder 76 as guided by the third airblow guide member 240H and then flows into the outer space 240C of theheating furnace 240 through the gap between the third air blow guidemember 240H and shoulder 76.

The entire primary blow molded article 70 except the bottom 74 isincreased in degree of crystallization as temperatures rise at thebarrel 72 and the shoulder 76, which are to be stretched during thesecond blowing molding, is accelerated, thus making such portionsadequately resistant against heat. Further, since hot air is ejectedlongitudinally of the primary blow molded article 70, it is possible tobring hot air into touch with the barrel 72 and the shoulder 76 of theprimary blow molded article 70 circumferentially uniformly, so thatcircumferentially uniform density also can be obtained.

In a comparative example, if hot air is ejected horizontally of theprimary blow molded article 70, uniform air ejection over the entirecircumference of the barrel 72 is difficult to achieve, and uniform heatdistribution over the circumference cannot be secured as hot airreflected by the barrel 72 undergoes mutual interfering. As a result,non-uniform circumferential thermal shrink can be achieved so that theless shrunk part of the primary blow molded article would be sandwichedbetween the parting surfaces of the blow mold during the secondary blowmolding. To the contrary, when hot air is blown vertically of theprimary blow molded article, no part can be sandwiched between theparting surfaces.

In this embodiment, the direction of blowing hot air is upward from thelower side of the primary blow molded article 70. Alternatively, it maybe downward from the upper side of the primary blow molded article 70.

FIG. 4 shows the structure of the heating furnace in this case. In thestructure of FIG. 4, the hot air from the hot air blow generator 240F isintroduced inside the partition 240A downwardly to the shoulder 76 ofthe secondary blow molded article 70 en route outside of the partition240A. The hot air is driven to flow vertically from the shoulder 76 ofthe primary blow molded article 76 and is guided downwardly by thepartition 240A while touching the shoulder 76 and the barrel 72. In thiscase, the guide members 240G, 240H of FIG. 2 may be omitted.

With this arrangement, since hot air does not touch the bottom 74 of theprimary blow molded article 70 even in the absence of the second airblow guide member 240G, it is possible to prevent the bottom 74 fromexperiencing crystallization and hence whitening. In the primary blowmolded article 70, it is possible to increase the degree ofcrystallization by increasing the density of material at the shoulder 76whose stretching ratio is low.

FIG. 5 shows a modified form of the heating furnace structure. As shownin FIG. 5, the first air blow guide member 240A is a double-sidewallstructure composed of inner and outer sidewalls 240A1, 240A2 with ahollow interior. The upper ends of sidewall 240A1, 240A2 are connectedto each other to seal. The inner sidewall 240A1 is connected at itslower end to the second air blow guide member 240G facing the bottom 72of the primary blow molded article 70 to mask the bottom 72. The outersidewall 240A2 is connected at its lower end to the air pipe 240D. Thesidewall 240A1 facing the primary blow molded article 70 has a pluralityof hot air ejection holes 240A3 inclined in such a direction as tocreate hot air flow vertically along the primary blow molded article 70.In this case, the ejection holes 240A3 are directed upwardly so that hotair flows upwardly along the primary blow molded article 70.

According to this structure, it is possible to prevent whitening of thebottom of the article, to cause uniform temperature distribution in thecircumferential direction of the article, to increase the wind speed ofhot air by narrowing hot air flow with the ejection holes 240A3, and toincrease the heat conduction speed at the circumferential wall of thearticle.

FIG. 6 shows the crystal densities at various portions when experimentswere conducted with the structure of FIG. 5. As is apparent from theexperimental data, it is certain that the degree of crystallization ofthe shoulder of the article is increased and that fluctuations in degreeof crystallization is reduced at every individual portion in thecircumferential direction.

According to the foregoing embodiments, during the heat treatment to becarried out before the second blow molding, hot air is blown verticallyalong the primary blow molded article 70 to increase the heatconductivity causing the increase of amount of heat to be received bythe primary blow molded article 70, so as to shorten the temperaturerising time of the primary blow molded article. Therefore, the length ofheating travelling path or the cycle time is reduced so that the moldingapparatus can be prevented from becoming larger in size.

On the other hand, in this embodiment, there is provided a structure forobtaining a heat-resistant container free of fins. This structure willnow be described as follows.

As shown in FIG. 1, sidewardly of the heating furnace 240 of the fifthheating station 240E situated upstream of the second blow moldingstation 30, a container width reforming means 40 is located, whosestructure is shown in FIGS. 7 to 9.

In FIG. 7, the outer wall and partition 240A of the heating furnace 240situated in the fifth heating station 240E has an opening 240I. Oppositeto the opening 240I, the container width reforming means 40 equippedwith a reforming guide 42 movable into and out of the heating furnace240 is located. The heating furnace 240 is identical in constructionwith the heating furnace arranged in the first to fourth heatingstations 240A to 240D, except that it has an opening 240I.

The container width reforming means 40 makes the outside diameter of thethermally shrunk article 80 in the heating furnace 240 smaller than theoutside diameter of the secondary blow molded product 90.

As shown in FIG. 7, the container width reforming means 40 includes, asmain components, reforming guides 42, a drive 45, 46, 48 for driving thereforming guides 42 into and out of the heating furnace 240, and a valvedrive mechanism 460 for canceling the increase of internal pressure ofthe thermally shrunk molded article 80.

In FIG. 8, the container width reforming means 40 has five reformingguides 42 for pressing opposite side surfaces of four articles 80 toreduce them in dimension in the direction of arrangement. Each reformingguide 42 is fixedly connected at its base to a reciprocating plate 44and has a taper surface 42A on a front end extending toward the opening240I of the heating furnace 240. The vertical shape of the front endportion, as partially shown in FIG. 9, is such that its upper part isformed on an inclined surface 42B along the shape of the shoulder of thesecondary blow molded product 90 while its lower part is formed as around portion 42C approximate to the shape of the heel of the secondaryblow molded product 90, there being a vertical wall surface 42D betweenthe upper and lower parts. Therefore, the reforming range of thereforming guides 42 covers from the shoulder to heel of the thermallyshrunk article 80. On the surface of each reforming guide 42, a removinglayer such as of Teflon (trade name) is formed to prevent the reformingguide 42 from sticking to the thermally shrunk article 80 when it isretracted from the article 80, so that the surface of the article willbe prevented from being scratche.

Further, in FIG. 8, the pitch (L) of arrangement of the individualreforming guides is set to a value equal to the pitch (L1) ofarrangement of the articles 80. The distance X between adjacent surfacesof the reforming guides 42 is a dimension by which the outside diameterX1 of the inadequately shrunk article 80 is to be corrected to a smalleroutside diameter X2(X=X1>X2). The dimension in the direction ofarrangement of the articles 80 is the dimension in the directionparallel to the parting surfaces of a second blow mold. Therefore, ifthe shrunk dimension X1 is set to a value smaller than the horizontaldimension of the cavity of the secondary blow mold, no part of thearticle will not be sandwiched between the mold halves of the secondblow mold.

The drive for the reforming guides 42 includes an air cylinder 45 havinga piston 45A (FIG. 8) which is fixed to the rear surface of thereciprocating plate 44. The stroke (S) of the piston 45A is set to avalue such that the reforming guides 42 can come into the spaces betweenthe articles and to a position confronting to the outermost sidesurfaces. A pair of guide rods 46 is fixed to the reciprocating plate 44and is supported by a support bracket 48 fixed on a base. Thereciprocating plate 44 is thereby guided so as to be movable in adirection perpendicular to the direction of arrangement of the articles80.

Therefore, the reforming guides 42, as indicated by broken lines in FIG.8, can come into the spaces between the thermally shrunk articles 80 andto the opposite sides of the outermost thermally shrunk articles 80, 80,and can be retracted from the inserted position to a position(solid-line position in FIG. 8) as not to obstruct the movement of thearticles 80.

The air cylinder 45 is set to an operative position by a non-illustratedcontrol means which inputs a signal from a detector (not shown) fordetecting whether the thermally shrunk articles confront the containerwidth reforming means 40. After the lapse of slight time delay from thesignal input, the control means outputs to the air cylinder 45 aninstruction for driving the reforming guides 42 forwardly. During thistime delay, the valve drive mechanism 460 assumes a standby position,whereupon it shifts to its position in which the increase of interiorpressure of the thermally shrunk article is canceled.

On the base at the side of the container width reforming means 40, thevalve drive mechanism 460 is mounted for releasing the increase ofinterior pressure from the article 80 during the reforming when theinterior pressure of the article 80 is increased.

A cap member 300 for holding the neck of the article 70, 80, 90airtightly will described. As shown in FIG. 7, the cap member 300 has anair blow supply passageway 302 for supplying pressurized air during thesecond blow molding, and an air leak passageway 304 for leaking air inthe article to adjust the internal pressure during the heating. The airblow supply passageway 302 is equipped with a valve 308 which is urgedby a spring 306 to normally close the passageway 302.

The valve drive mechanism 460 drives the valve 308 to open, when theside surfaces of the article 80 is pressed by the reforming guides 42,to leak air so that the internal pressure of the article 80 is preventedfrom rising in response to the pressure.

The valve drive mechanism 460 of FIG. 7 includes an air cylinder 74supported by a fixed support 170 mounted on the base, and an airextractor rod 76 fixed to the outer end of the piston of the aircylinder 74. The valve drive mechanism 460 causes the air extractor rod76 to project toward the valve 308, during the reforming of thethermally shrunk article 80, to open the valve 308 against the spring306.

The period of projection of the air extractor rod 76 is set by thecontrol means. In this embodiment, this projection starts when fourarticles 80 are brought to a position confronting the container widthreforming means 40. The air extractor rod 76 keeps the projectedposition to hold the valve 308 open until the reforming guides 42 areremoved from articles 80.

In this embodiment, pivotally movable reforming guides adapted to bearranged between the articles 80 may be substituted for the reformingguides each having the reciprocatingly movable taper surface. Further,the reforming guides may be equipped with a temperature control means,such as a heater or a cooler, so that the article at part touching thereforming guides 42 will be prevented from being excessively cooled orheated.

In this embodiment, a structure for preventing the mold from beingopened is provided. This structure will now be described in detail.

Generally, in the blow molding, such as shown in FIG. 12, the preventingstructure includes a hydraulic actuator 110 mounted on the rear surfaceof a mold clamp disc 100 supporting a blow mold 100A. The opening andclosing operation and the clamping operation for the blow mold 100A areperformed by the same hydraulic actuator 110.

In order to prevent the mold from being opened during the blow molding,a structure for locking the mold in closed position is used. As shown inFIG. 13A, a lock means 120 includes a pair of engaging members inopposite ends of engaging recesses of the blow mold 100A, and a pair ofengaging members to be received in the respective engaging recesses. Inthe blow molding, the blow pressure will increase remarkably high.Therefore it is necessary to prevent the blow mold from being openedagainst the blow pressure. If a hydraulic actuator is to be used toclamp the mold, the diameter of a piston inserted into the cylinder ofthe hydraulic actuator must be large enough to produce a great clampingforce. In the case of a large-diameter cylinder, since a great quantityof oil is necessary to close and open the mold quickly, large impactforce also would act when the mold halves strike against each other. Ifsuch collisions are repeated during the molding, the mold will undergofatigue considerably. On the other hand, the lock means is necessary todetour the narrow space between the rotary disc and the base when thearticle is blow molded as suspended and held on the rotary disc.

Consequently, for example, if a pressure larger than a predeterminedclamping force is required as the container cross-sectional area is verylarge, or if the container to be formed is of a type difficult to shape,the blow pressure will surpass the clamping force occasionally. Whenthis phenomenon happens if the number of articles to be molded at onceis large, the length of the blow mold is necessarily long so that theblow mold would tend to be bent centrally, as indicated bydash-and-two-dot lines in FIG. 13B. Therefore, even using the lockingmeans, it occasionally happened that the closed mold could not bereliably prevented from being opened during the molding. If the mold isthus opened, part of the article would be sandwiched between the partingsurfaces of the blow mold to project as fins on the final product.

FIGS. 10 and 11 show a blow mold clamping means 130 located in thesecond blow molding station and equipped with a blow mold composed of apair of mold halves which are openable and closable radially of therotary disc 22.

The clamping means 130 includes mold support bases 132, an air cylinder134, a mold clamping member 136, and a lock member 138.

The mold support bases 132 close to sandwich the primary blow moldedarticle 70 hanging from the rotary disc 22 and are movable toward andaway from each other. In this embodiment, a structure for moving themold support bases 132 toward and away from each other includes a pairof racks 140, 142 and pinion 144. The racks 140, 142 are slidablymounted and guided on the base of the oven blow molding apparatus 10,meshing the pinion 144.

In order to move the racks 140, 142, the air cylinder 134 constituting ahigh-speed actuator is connected to one of the mold support bases 132.The air cylinder 134 is set up for the initial position in which thepiston 134A is retracted. Therefore, while the initial position of theair cylinder 134 is set, the mold support bases 132 are situated inpositions remote from each other, opening the blow mold 50. Thehigh-speed actuator in this embodiment is set up for a value higher thana plunger 136A of the mold clamping member 136.

The mold clamping member 136 is fixed to the upper surfaces of the moldsupport bases 132. Inside the mold clamping member 136, there aremounted the plunger 136A constituting the drive rod for clamping theblow mold 50, and the lock member 138 for locking the mold clampingmember 136 in locked position.

The plunger 136A projects outwardly from the mold clamping member 136 ata number of positions or opposite positions in the longitudinaldirection of the blow mold 50, and the base of the plunger 136A is fixedto the piston 136B inserted into a chamber of the mold clamping member136. A mold base plate 52 to which the blow mold 50 is fixed is attachedto the front end of the plunger 136A. The confronting spaces eachsandwiched between the pistons 136B in the chamber are filled with anon-compressive fluid such as oil; as the supplying and discharging ofthe non-compressive fluid between the spaces are controlled, the pistons136B will be reciprocatingly moved.

In this structure, the mold support bases 132 are located in closedposition in which the parting surfaces of the blow mold 50 slightlytouch each other, and when the lock member 138 is being locked, thepistons 136B project. Therefore, as the pistons 136B project, theparting surfaces of the blow mold 50 are pressed to clamp the mold. Thepressure to be used for clamping is set to at least 40 kg/cm². Thestroke of the piston 136A is set to a value substantially equal to thesum of the gap between the rod 138B of the lock member 138 and therotary disc 22 and the gap between the rod 138B and the base,particularly a very small stroke of 0.3 to 0.4 mm.

The lock member 138 has a rod 138B fixed to the piston 138A insertedinto the chamber in the mold clamping member 136. The rods 138B arearranged at the upper and lower sides of the mold clamping member 136and are movable toward and away from the base and the rotary disc 22 inresponse to the reciprocating movement of the piston 138A. The lockmembers 138 have a function of locking the mold support bases 132 inclosed position of the blow mold 50 by engaging the fitting portions 26formed in the rotary disc 22. When blow pressure is loaded afterclamping, the mold is kept closed under the blow pressure.

Inside the chambers in which the pistons 138A are received, theconfronting spaces sandwiched between the pistons 138A are filled withair; the rods 138B are vertically moved toward and away from each otheras the supplying and discharging air into and out of the spaces iscontrolled. This controi takes place based on that the rods 138B areinserted into the fitting portions 26 when the mold support bases 132are closed.

In each fitting portion 26, a substance is fitted in a hole formed inthe rotary disc 22 so that the rotary disc 22 is prevented from beingdamaged when the rods 138B strike the substance in the hole.

Reference numeral 54 in FIG. 10 designates a rod having a function ofrestricting the shrinkage and centering while the primary blow moldedarticle is being thermally shrunk; 56, a bottom template of the blowmold 50; and 58, a blow core connected to a holder and mounted in acheck valve for allowing a pressurized fluid in the direction of supply.

With this structure, the mold support bases 132 can be moved, by the aircylinder 134 connected to one mold support bases 132, at high speed toclosed position in which the parting surfaces of the blow mold 50faintly strike against each other. When the molded support bases 132 aremoved to the closed position, the rod 138B of the lock member 138 islocked with respect to the fitting portions 26 of the rotary disc 22 andthe base by the air supply/discharge control. Therefore, when it isdetected that the mold support bases 132 have been moved to apredetermined position and that the rock member 138 has been locked, themold clamping members 136 are moved, by means for supplying anddischarging non-compressive fluid such as oil, with a stroke smallerthan the opening and closing stroke of the blow mold 50, to press theparting surfaces of the blow mold 50 against each other. Now, when thesecondary blow molding takes place for the thermally shrunk article 80placed in the blow mold 50, the blow pressure acts on the blow mold 50.By this pressure, the lock members 138 are received by the fittingportions 26 of the rotary disc 22 and the base, and the mold clampingmembers 136 are held in the clamping position.

Upon termination of the secondary blow molding, the pressure to the blowmold 50 is freed by non-compressive fluid supply/discharge control inthe mold clamping members 136, and then the rods 138B of the lockmembers 138 are unlocked. Then the air cylinder 134 restores theoriginal position.

According to this structure, partly since the mold support bases forclosing and opening the mold are driven to move toward and away fromeach other at high speed using the air cylinder, and partly since themold clamping members having a stroke smaller than the stroke of themold support bases are driven using non-compressive fluid, it ispossible to perform the closing and opening of the mold quickly.Further, since the stroke using non-compressive fluid is reduced, themechanism using such fluid can be reduced in size. Since locking by therotary disc and the base takes place vertically of the mold supportbases, it is possible to prevent the mold from being opened even whenthe blow pressure is exerted on the mold in the opening direction.

In this embodiment, the apparatus is also equipped with a structurewhich makes the final product discharge means simple in structure andperforms accurate sorting.

The discharge station 14, as shown in FIGS. 1 and 14, has a dischargemeans 18. The discharge means 18 is a chuck which supports the lowersurface of a support ring formed on the neck of the secondary blowmolded product 90 and which discharges the secondary blow molded product90 out of the travelling path on the rotary disc 22. A conveying guide241 is situated at the product discharge position, constituting part ofthe article discharge path. A pivotable guide 242 is situated oppositeto the conveying guide 241. The conveying guide 241 is in the form of aflat plate attached to the upper surface of a guide support 244 fixed onthe base.

The pivotable guide 242 is pivotally movable between a retractedposition (dash-and-two-dot-line position in FIG. 14) and anotherposition in which the guide 242 supports the side surface of the neck ofthe secondary blow molded product 90. Before the discharge means 18,which has discharged the product 90, is returned from the broken lineposition to the solid-line position in FIG. 14, the pivotable guide 242comes in contact with the side surface of the neck of the secondary blowmolded product 90 to prevent the secondary blow molded product 90 fromfalling down.

On the upper surface of the conveying guide 241, a moving means 250 forthe secondary blow molded product 90 is situated.

The moving means 250 moves the products 90 in opposite direction in thesame line along the discharge path 14A, based on the reference ofselection of secondary blow molded articles 90 discharged onto theconveying guide 241.

The moving means 250 is equipped with a double-step air ejection nozzleheader 250A, 250B laminated on the upper surface of the conveying guide241. The air ejection nozzle headers 250A, 250B, as shown in FIG. 15,have nozzles inclined in opposite directions by such an angle as toobtain a component force for moving the secondary blow molded articles90 along the extension of the discharge path 14A.

Each of the air ejection nozzle headers 250A, 250B has an air chambercommunicating with nozzles. To this air chamber, an electromagneticallypowered three-way switch valve 256 is connected via, for example, pipes252, 254. The three-way switch valve 256 is located at a position forshutting out the communication between the individual pipes 252, 254 andan air pump 258. The three-way switch valve 256 is operatively connectedwith a control unit 260 for selectively setting the communicationbetween the air pump 258 and the individual pipes 252, 254.

The control unit 260 includes a moving control means for controlling thedirection of moving the secondary blow molded articles as finalproducts; the main part of the control unit 260, for example, isconstituted by a micro computer.

To the input side of the control unit 260 via a non-illustrated I/Ointerface, there are connected a sensor 262 for detecting the number ofprimary blow molded articles 70 supplied from the conveying station 12and held in one block of the rotary disc 22, and a gap sensor 264 fordetecting the gap between the parting surfaces in the mold clampingmeans 30 during the secondary blow molding. To the output side of thecontrol unit 260 via the I/O interface, there are connected a drivemeans 266 for the three-way switch valve 256. Of the foregoing sensors,the sensor 262 may be, for example, an optical sensor, and the gapsensor 264 may be, for example, an optical sensor or a piezoelectricsensor for detecting a pressure between the parting surfaces. Inaddition to these sensors, for instance, if a neckpiece is to beinserted into an injection cavity mold during injection molding of apreform, an optical sensor (not shown) for detecting whether theneckpiece is removed may be connected to the input side of the controlunit 260.

In the control unit 260, as the reference of selection for the finalproducts, normal/abnormal discrimination results using the outputs fromthe foregoing sensors 262, 264 are used. The case where abnormal moldingtakes place is exemplified: the case where the number of primary moldedarticles does not reach the hold numbers of the rotary disc 22; the casewhere mold matching in the blow mold clamping means 30 is notappropriate; or the case where the neckpiece is removed. In such case,the three-way switch valve 256 will be energized to supply air to theair ejection nozzle headers as set up in the direction of dischargingthe abnormal article. When it has been discriminated from the outputsfrom the sensors 262, 264 that no abnormal molding took place, air willbe supplied to the air ejection nozzle headers as set up in thedirection of discharging normal articles.

In this structure, the moving direction for the secondary blow moldedarticles 90 whose necks are held by the pivotal guide 242 is determinedby the convconveying guide 241 in the discharge station 14 and themoving means 250. Therefore, since the control unit 260 previouslydetermines the moving direction based on the output signals from thesensors 262, 264, it will be determined according to the previousdetermination whether or not air should be supplied to the air ejectionnozzle headers 250A, 250B of the three-way switch valve 256. Therefore,when the secondary blow molded product 90 moved to the discharge station14 is obtained by normal molding, the moving direction for qualifiedarticles will be set by the air ejection nozzle headers 250A, 250B. Whenit is obtained by abnormal molding, the moving direction for faultarticles will be set by the air ejection nozzle headers 250A, 250B. As aresult, the secondary blow molded articles 90 will be blown away on thedischarge station 14 by air ejection from any one of the air ejectionnozzle headers and will then be conveyed to a predetermined storingunit.

In the foregoing structure, a two-way switch valve may be substitutedfor the three-way switch valve. For instance, if the final products areto be packed in a box, a counter for counting the total number of thesecondary blow molded articles discharged for storage may be connectedto the input side of the control unit. Therefore, using the counter, itis possible to prevent the secondary blow molded articles fromoverflowing. According to such structure, the sorting of finally moldedarticles can be performed by selecting the direction of discharging thearticles of opposite directions in the same line on the dischargestation. It is therefore possible to sort normal articles and abnormalarticles using the existing discharge station, without making theapparatus large in size and complex in structure.

What is claimed is:
 1. A method of forming a heat-resistant container,comprising the steps of:(a) introducing a primary blow molded articleinto a heating furnace having a pair of first air blow guide membersseparated by a traveling path of the primary blow molded article andconveyinq the primary blow molded article along the traveling path; (b)thermally shrinking the primary blow molded article by exposing theentire circumferential surface of a barrel portion of the primary blowmolded article to hot air having a temperature high enough to facilitatecrystallization of the primary blow molded article by blowing the hotair from one end of the furnace inside said pair of first guide memberslongitudinally along the primary blow molded article as the primary blowmolded article is conveyed along the traveling path; and (c) secondaryblow molding the thermally shrunk primary blow molded article in acavity of a secondary blow mold composed of a pair of mold halves,thereby shaping the primary blow molded article into the heat-resistantcontainer.
 2. A heat-resistant container forming method according toclaim 1, wherein said thermally shrinking step includes heating with hotair a plurality of primary blow molded articles transferred at regularintervals within the heating furnance synchronized with everytermination of said secondary blow molding, and blowing hot air from ahot air source to the primary blow molded article longitudinally fromone end to the other inside said pair of first air blow guide members.3. A heat-resistant container forming method according to claim 2,wherein said thermally shrinking step further includes blowing hot airfrom a bottom portion of the primary blow molded article, and guidinghot air to the barrel portion of the primary blow molded article by asecond air blow guide member for masking the bottom of the primary blowmolded article in the heating furnace so as not to expose the bottomdirectly to hot air, and returning the hot air, after touching thebarrel, to the hot air source via the outside of the first air blowguide members from a side remote from the bottom.
 4. A heat-resistantcontainer forming method according to claim 2, wherein said thermallyshrinking step further includes guiding hot air along a shoulder of theprimary blow molded article by a third air blow guide member which issituated around and sloping alongside the shoulder.
 5. A heat-resistantcontainer forming method according to claim 2, wherein said thermallyshrinking step further includes returning the hot air, after flowing thehot air longitudinally along the barrel and past the shoulder, to thehot air source via the outside of the first air blow guide member.
 6. Aheat-resistant container forming method according to claim 2, whereinsaid introducing step includes introducing a plurality of primary blowmolded articles as a set simultaneously into the heating furnace, saidthermally shrinking step includes heating a plurality of sets of primaryblow molded articles placed in the heating furnace, introducing each setof primary blow molded articles upon every termination of said secondaryblow molding step, discharging a leading set of primary blow moldedarticles out of the heating furnace, and introducing a new set ofprimary blow molded articles into the heating furnace, and wherein saidsecond blow molding step includes secondary blow molding simultaneouslythe set of primary blow molded articles discharged out of the heatingfurnace.
 7. A heat-resistant container forming method according to claim6, wherein said thermally shrinking step further includes controlling atotal heating time, which is a heating time necessary to obtain a degreeof crystallization of at least 1.373 g/cm³ for the barrel of a singleprimary blow molded article in the heating furnace, by varying the windspeed and/or temperature of hot air.
 8. A heat-resistant containerforming method according to claim 6, wherein said thermally shrinkingstep includes blowing the hot air, whose temperature is sufficient tofacilitate crystallization of the primary blow molded article, at a windspeed of at least 0.6 m/sec, and setting the total heating time to atmost one minute, which is a heating time necessary to obtain a degree ofcrystallization of at least 1.373 g/cm³ for the barrel of a singleprimary blow molded article in the heating furnace.
 9. A heat-resistantcontainer forming method according to claim 8, wherein said thermallyshrinking step is performed with setting the temperature of hot airwithin a range of 230° to 260° C. and the wind speed of hot air within arange of 0.6 to 4.0 m/sec.
 10. A method of forming a heat-resistantcontainer, comprising the steps of:(a) introducing a primary blow moldedarticle into a heating furnace; (b) thermally shrinking the primary blowmolded article by exposing the entire circumferential surface of abarrel portion of the primary blow molded article to hot air having atemperature high enough to facilitate crystallization of the primaryblow molded article by blowing the hot air longitudinally along theprimary blow molded article, wherein said thermally shrinking stepfurther includes reforming the outer diameter of the primary blow moldedarticle in a direction parallel to parting surfaces of mold halves of asecondary blow mold to have a diameter smaller than the transverse widthof the cavity of the mold halves by pressing facing sidewalls of thebarrel portion of the primary blow molded article inwardly; and (c)secondary blow molding the thermally shrunk primary blow molded articlein a cavity of the secondary blow mold thereby shaping the primary blowmolded article into the heat-resistant container.
 11. A heat-resistantcontainer forming method according to claim 10, wherein said thermallyshrinking step further includes releasing an increasing inner pressurefrom the interior of the first blow molded article, when the sidewallsof the primary blow molded article are inwardly pressed, while saidreforming step is performed with maintaining the inner pressure of theprimary blow molded article at a predetermined value.
 12. A method offorming a plurality of heat-resistant containers, comprising the stepsof:(a) introducing a plurality of primary blow molded articles as a setsimultaneously into a heating furnace; (b) thermally shrinking the setof primary blow molded articles by exposing the entire circumferentialsurface of a barrel portion of each of the primary blow molded articlesto hot air having a temperature high enough to facilitatecrystallization of each primary blow molded article by blowing the hotair longitudinally along the primary blow molded article, wherein saidthermally shrinking step includes inserting reforming means for pressingthe facing sidewalls of the barrel portion of each primary blow moldedarticle inwardly, along opposite sides of each primary blow moldedarticle in the direction of arrangement of one set of primary blowmolded articles, and reforming the outer diameter of each of the primaryblow molded articles in a direction parallel to parting surfaces of moldhalves of a second blow mold to have a diameter smaller than thetransverse width of the cavity of the mold halves; and (c) secondaryblow molding the set of thermally shrunk primary blow molded articles ina cavity of the secondary blow mold composed of the mold halves, therebyshaping the set of primary blow molded articles into the heat-resistantcontainers, wherein said thermal shrinking step further includes heatinga plurality of sets of primary blow molded articles placed in theheating furnace, introducing each of the primary blow molded articlesinto the heatinq furnace after said second blow molding step,discharging a leading set of primary blow molded articles out of theheating furnace, and introducing a new set of primary blow moldedarticles into the heating furnace.
 13. A heat-resistant containerforming method according to claim 12, wherein said reforming stepincludes temperature-conditioning the reforming means to prevent theprimary blow molded articles at portions in contact with the reformingmeans from being excessively cooled or heated.
 14. A heat-resistantcontainer forming method according to claim 12, wherein said thermallyshrinking step further includes releasing an increasing inner pressurefrom the interior of the primary blow molded articles, when thesidewalls of the primary blow molded articles are inwardly pressed,while said reforming step is performed with maintaining the innerpressure of the primary blow molded articles at a predetermined value.15. A heat-resistant container forming method according to claim 1,further comprising, after said secondary blow molding step, introducingthe heat-resistant containers, which are taken out of the secondary blowmold, in opposite directions in the same line using a nozzle forejecting air in opposite directions in the same line.